Many modern pocket sized devices exist and are being developed that contain or have access to very sensitive information. Examples include cellular phones that can access a cellular network, smart cards, and other hand held pocket sized devices. If misappropriated, such devices can give an unauthorized user free phone system access, access to private telephone numbers and contact information, internet access, and access to other sensitive information. To improve security, fingerprint sensors are highly useful, however the size and cost of such sensors is often prohibitive in such very small, low-cost devices.
Although any type of fingerprint sensor with suitable size and robustness characteristics can be used for these applications, one class of fingerprint sensors that are particularly useful for ultra-small, low-cost devices are deep finger penetrating radio frequency (RF) based sensors. These are described in U.S. Pat. Nos. 7,099,496; 7,146,024; and U.S. Patent Publications US 2005/0244038 for “Finger Position Sensing Methods and Apparatus” to Benkley (now U.S. Pat. No. 7,463,756); US 2006/0083411 for “Finger Sensing Assemblies and Methods of Making” to Benkley; US 2005/0244039 for “Methods and Apparatus for Acquiring a Swiped Fingerprint Image” to Geoffroy and Buxton; and US 2007/0031011 for “Electronic Fingerprint Sensor with Differential Noise Cancellation” to Erhart, Keyvani, Benkley, and Jandu (now U.S. Pat. No. 7,460,697) and contents of these patents and patent applications are incorporated herein by reference. These types of sensors are commercially produced by Validity Sensors, Inc, San Jose Calif. This class of sensor mounts the sensing elements on a thin, flexible, and environmentally robust support, and the IC used to drive the sensor resides in a protected location some distance away from the sensing zone. Such sensors are particularly advantageous in applications where small sensor size and sensor robustness is critical.
Smart cards are an excellent example of a pocket sized, low-cost, portable device where fingerprint sensors would be particularly desirable. Smart cards are electronic devices, typically in the shape of a conventional wallet-sized thin rectangular credit card. Smart cards typically contain active electronic components, such an internal processor and secure memory, which is used to hold sensitive information. Smart cards are often used for financial transactions, such as purchasing products and services, or depositing or retrieving money from financial institutions. As a result, smart cards can be viewed as a portable means of transferring money, and in fact can be considered to be a higher functionality version of a credit card. Throughout this disclosure, the term “smart card” will be considered to also include such higher functionality credit cards as well. The incentive for unscrupulous users to illegitimately acquire and falsify smart cards (and smart credit cards) is thus quite high, and methods and systems to ensure smart card security are quite desirable.
One of the major ways that a smart card can be misused is through physical theft, where a smart card simply falls into the hands of an unauthorized user. Another common security breech is through electronic or security number theft, where the card itself is not misplaced, but its corresponding identification numbers and codes fall into the wrong hands.
In theory, both types of security breech may be prevented by incorporating fingerprint sensors into the smart card. If such sensors were present, legitimate users could verify their identity upon initial receipt of the card, and at certain key times thereafter, by fingerprint swipes. Although attractive, the technical challenges of implementing fingerprint sensors into smart cards are substantial. Although other sizes are quite possible, smart cards are often designed to meet the ISO/IEC 7810 standard for identification cards, such as the ID-1 standard which typically calls for thin credit-card-like rectangular dimensions of 85.60×53.98 mm (3⅜″×2⅛″) and thicknesses of only 0.76 mm (approximately 0.03″). Even if the thickness specification is relaxed to several mm, such as 5 mm or less, Fitting a fingerprint scanner and associated circuitry into such a small space is challenging. An additional problem is that smart cards typically are subjected to demanding environmental conditions, such as being stored and retrieved from a wallet for extended periods of time, any sensor and circuitry on such cards must be extremely robust.
Consider the engineering challenges: not only must the fingerprint sensor itself be paper thin and robust (which rules out many types of conventional but bulky or fragile fingerprint sensors), but the associated electronic circuitry, such as the processor, memory, any display device, electrical contact or communication device, and any battery used to power the unit must also be extremely thin. Small and thin batteries have correspondingly low amounts of stored energy. For example, a typical miniature battery might have a power capacity of only between 15 and 30 milliamp hours. Thus, in addition to small sensors, efficient sensor and sensor circuitry power utilization are also critical.
Here ergonomic factors also come into play. When not reading a fingerprint swipe, the smart card's fingerprint sensors and circuitry can be in a hibernation state and draw minimal amounts of power. However when reading a fingerprint swipe, fingerprint scanners require appreciable amounts of power. For example, a fingerprint scanner might draw 100 milliamps for two seconds during a swipe. For a 15 milliamp hour battery, the total reserve power is 54,000 milliamp seconds. Each swipe might consume as much as 200 milliamp seconds of power. Thus in some scenarios, a smart card's battery might be totally used up after only 270 fingerprint swipes.
Unfortunately improper fingerprint swipes often use as much power as proper fingerprint swipes. If, due to ergonomic issues, a user has to make repeated attempts to obtain a valid fingerprint swipe, battery life would suffer, and the practicality of such a smart card for routine, long-term, use would become minimal. Thus methods and devices to read fingerprint swipes quickly, accurately, and with minimal need for repeats due to improper user technique are highly useful.
Returning to the discussion of fingerprint sensing devices, a number of devices and techniques exist for sensing, capturing, and reconstructing the image of a fingerprint as it moves across a sensor array. Though many devices exist to sense and record an entire fingerprint, these devices tend to be relatively large. To save space and to be compatible with small portable devices, partial fingerprint sensing devices, such as the previously discussed Validity sensors, have been developed.
Partial fingerprint sensing devices have a sensing area that is smaller than the fingerprint area to be imaged. This is desirable because this type of sensor takes up much less space than a full fingerprint sensor, but to function properly, the user must move his finger and manually “swipe” it across the sensing area.
These sensing devices generally consist of one or more one-dimensional imaging arrays of sensors (imaging lines) disposed perpendicular to the axis of motion. For example, one common configuration used for a fingerprint sensing surface includes CCD (charge coupled devices) or C-MOS circuits. These components are embedded in a sensing surface to form a matrix of pressure sensing elements that generate signals in response to pressure applied to the surface by a finger. These signals are read by a processor and used to reconstruct the fingerprint of a user and to verify identification. Other devices include a matrix of optical sensors that read light reflected off of a person's finger and onto optical elements. The reflected light is converted to a signal that defines the fingerprint of the finger analyzed, and is used to reconstruct the fingerprint and to verify identification. As previously discussed, more modern devices, such as the Validity fingerprint sensors, are based on static or radio frequency (RF) devices configured to measure the intensity of electric fields conducted by finger ridges and valleys, such as deep finger penetrating radio frequency (RF) based sensing technology, and use this information to sense and create the fingerprint image.
As the finger surface is moved across the sensor, portions of the fingerprint are sensed and captured by the device. These data from these various portions is usually then stored in memory (working memory), and reconstructed using an electronic processor, such as a microprocessor, into a mosaic or overlapping image that recreates the entire fingerprint. Often the processor will then compare this mosaic image in working memory with an authorized fingerprint stored in fingerprint recognition memory, and determine if there is a match or not. If there is a match, the processor may then allow sensitive information (financial data, security codes, etc.) stored in secure memory to be accessed by external devices.
As might be imagined, this process of scanning and fingerprint reconstruction requires extensive processing resources for retrieving the partial fingerprint data and running the algorithms need to reconstruct the entire fingerprint. Again this takes electrical power, which is problematic when battery size is limited. Thus again, methods and devices to improve the efficiency of this process are desirable. In particular, user interfaces, designs, and systems that encourage correct finger swipes are critical.
For example, in swipe sensors used for fingerprint imaging, it is important that a user properly align the finger along with the fingerprint sensor so that a high quality image can be captured. If, for example, a user swipes the finger at one or more improper angles, a poor fingerprint image may be captured. At a minimum, additional computational time and energy will be needed by any processor that attempts to interpret the image, and more likely, a rescan will be required, significantly lowering battery life and also inconveniencing the user.
Therefore, a need exists in the art for a useful fingerprint sensor system that can be incorporated in a small device, such as a smart card, that operates without excessive size, power, or processing computational resources. There further exists a need in the art for user interfaces and guidance devices to help insure that users will correctly use such devices. As will be seen, the invention accomplishes these functions in an elegant manner.